1. Field of the Invention
This invention is in the field of medical ultrasonic diagnostic equipment and more particularly relates to improved high resolution rotating head ultrasonic scanners particularly adapted for use in the scanning subsystem of an ultrasonic breast scanning system.
2. Description of the Prior Art
There are statistical data up to and including the early 1970's to the effect that there has been essentially no change in the death rate from cancer of the breast of American women. Early detection is the most significant factor in improving the probability of survival of a patient with breast cancer.
The primary methods of detecting cancerous growths within the breast are manual palpation, X-ray examination, which includes mammography and xeroradiography and thermography. Each of the foregoing techniques has its advantages but each has serious limitations with respect to its use for the early detection of breast carcinoma. Fry, E. K., Kossof, G., Hindman, H. A., Jr., The Potential of Ultrasonic Visualization for Detecting of Abnormal Structure Within the Female Breast, IEEE, Ultrasonic Symposium Proceedings, pp. 25-30, 1972.
In the early 1950's the potential for using ultrasound visualization systems to detect breast carcinoma was demonstrated. Some of the advantages of ultrasonic visualization techniques are that ultrasound is noninvasive, can be externally applied, is nontraumatic and is safe at the acoustical intensities and duty cycles encountered in existing diagnostic equipment. While the potential of ultrasound visualization of breast tissue has been recognized and the need for ultrasonic breast scanning instruments or systems is also recognized, the development of such instruments for clinical use in screening large numbers of patients has not heretofore been accomplished.
In order to detect as early as possible breast carcinoma, or precancerous conditions, the resolution of visualizations of the tissue scanned must be good. Such resolution is improved by not distorting the breast tissue during the examination. One way of accomplishing this is to have the patient's breasts freely floating in a liquid such as water, which liquid serves as the coupling medium for transmitting ultrasonic energy from a transducer to the tissue and reflections from transmitted pulses of such energy from sources within the tissue due primarily to changes in speed of transmission of the sound in the tissue back to the transducer. In addition, such an instrument should not cause the patient to suffer any discomfort and should require a minimum of time to prepare the patient for examination. Sucn an instrument should conduct an examination quickly and reliably without requiring highly skilled technicians or operators to operate the instrument.
In conducting an ultrasonic examination of breast tissue, it is important that the liquid level in the examination tank in which the patient's breasts are immersed be maximized so that the tissue under the patient's arms can be examined to detect the possibility of the spread of breast cancer. Prior art ultrasonic breast scanners in which the patient's breasts are immersed in a liquid have tried to confine the liquid by a liquid tight seal between the patient and the tank. A problem with such prior art breast scanners is that they have not been successful in minimizing the amount of liquid escaping from the examination tank during an examination.